DICOMdir

DICOMDIR is a DICOM directory information file used to organize a collection of DICOM files stored in a single directory or a directory tree. It serves as an index that enables software to navigate the data by patient, study, series, and image, rather than scanning the file system for individual files. This structure facilitates quick lookup and retrieval in viewers, workstations, and PACS.

The DICOMDIR file itself is a DICOM object that contains a Directory Record Sequence. The records are hierarchical and come in types such as PATIENT, STUDY, SERIES, and IMAGE. PATIENT records group related studies, STUDY records group related series, and SERIES records group related images. IMAGE records point to the actual DICOM files that store the image data, providing references to the files and the associated SOP information. While the DICOMDIR describes the data, the actual image data remains stored in separate DICOM files; the DICOMDIR does not embed image data.

Generation and usage: DICOMDIR is commonly created by imaging devices or by post-processing software when saving studies to media (such as CD/DVD) or to a directory intended for easy viewing. Many modern workflows can function without a DICOMDIR, relying instead on file-system queries or database indexes. When a DICOMDIR is present, its records must remain consistent with the referenced files; moving, altering, or deleting files typically requires regenerating or updating the DICOMDIR.

Limitations: DICOMDIR is most useful for media-based distribution and offline navigation. It is optional in many workflows, and inconsistent implementations can lead to compatibility issues if the directory structure or references are incomplete or incorrect. Overall, DICOMDIR remains a widely supported, legacy-friendly mechanism for organizing related DICOM files in a browsable, hierarchical way.